Method and construction for recording and retrieving information with an electron beam



Feb. 7, 1967 METHOD AND CONSTRUCTION FOR RECORDING AND RETRIEVING PI FRAM ET AL 3,303,341

INFORMATION WITH AN ELECTRON BEAM Filed May 25, 1964 /LZ 0019.155( E/V YER.

fan/Apo W REE@ Ja United States Patent O 3,303,341 METHOD AND CONSTRUCTION FOR RECORDING AND RETRIEVING INFORMATION WITH AN ELECTRON BEAM Paul Fram, Lincoln Township, Washington County, and Edward W. Reed, Jr., St. Paul, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed May 25, 1964, Ser. No. 369,906 Claims. (Cl. Z50- 65) corporated into such medium.

In another embodiment, this invention relates to recording information as with a scanning, modulated electron beam or light beam on the radiation-sensitive surface of such a medium. Thereafter, the so-scanned medium is subjected to known photographic development procedures to produce an image-wise pattern of silver deposits representative of the initial beam modulation. Finally, to retrieve the so-stored information, the resulting medium is exposed to electron excitation to produce differential photon emission.

In a typical recording operation in accordance with this invention, an electron beam modulated with informati-on to be recorded is moved in a pattern over the surface of a storage medium of the invention. This medium is then developed to leave surface deposits adjacent one surface thereof in a pattern coresponding to such electron beam modulation. Thereafter the so-recorded information is retrieved or read out by exposing a surface of the resulting medium to a beam of electrons typically moved in a pattern thereover which exposure causes a pattern of differential photon emission from said recorded medium. Such emission is sensed either optically or photoelectrically and converted into an output signal corresponding to the original information.

It is therefore among the objects of the present invention to provide an improved process for recording with modulated radiant energy and for readout with an electron beam, using conventional radiation-sensitive silver halide compositions.

It is another object of this invention to provide information storage media for electron beam recording which employ silver halide materials, scintillator compositions and conductive materials which are all well known 'and readily available.

It is another object of this invention to provide a medium of the class described which is at least light transmissive.

It is another object of this invention to provide a medium of the class described which is cap-able of high density recording and readout at densities say, in excess of 105 bits per square centimeter of surface area.

3,303,341 Patented Feb. 7, 1967 It is a further object of this invention to provide a process for making such media.

Other and further objects will be apparent to those skilled in the art from a reading of the present specification taken together with the drawings wherein:

FIGURE 1 is a cross-sectional diagrammatic View of an embodiment of a four-layered unexposed medium construction of this invention;

FIGURE 2 is a View similar to FIGURE l, but showing a three-layered construction wherein the fluorescent and support (or backing) layer Iare combined;

FIGURE 3 is a view similar to FIGURE 2, but showing the fluorescent backing and conductive layer, respectively interchanged;

FIGURE 4 is a view similar to FIGURE l, but shoW ing a semi-transparent conductive layer interchanged with the fluorescent layer;

FIGURE 5 is a view similar to FIGURE 2, but showing the backing layer combined with the conductive layer;

FIGURE 6 is a cross-sectional diagrammatic view illustrating the appearance of an embodiment of FIGURE 2 after both exposure to, for example, modulated, excited electrons and subsequent development; Iand FIGURE 7 is a view similar to FIGURE 6 illustrating the appearance the embodiment of FIGURE 4 may take after exposure to, for example, modulated, excited electrons and subsequent development.

A description of starting materials will now be given. As indicated above, media of the present invention generally contain a support or backing, an electron-sensitive silver halide emulsion, a fluorescent composition, and an electrically conductive material.

The backing material is generally nearly planar in form; that is, it has opposed generally parallel faces. Further, the backing material layer is grain-free. By the term grain-free as used in this specification, reference is had to particles which on the average Iare not greater than about 1 micron in maximum average dimension. Preferred backing materials are substantially transparent to photon energies associated with the characteristic photon emission from fluorescent material used in a medium construction of the invention, i.e., generally from about 2,000 to 10,000 A. (see below). Also, it is preferably substantially non-brous and preferably has substantially non-porous, smooth faces. It is further preferred to use organic, film-forming polymeric materials in ya homogeneous sheet-like form having a dimensional stability such that the co-eflicient of expansion for temperature and humidity shall not exceed 2x10*5 unit per unit per percent change in RH and per degree change in temperature over a relative humidity range of 20% to 80% and over a temperature range of +30 to -{-l30 F.

It is also preferred that the backing member have a roughness not greater than about 1.5 microiuches when measured by a so-called Micro Surf model smoothness gauge.

Chemically, the backing member can consist of organic or inorganic materials or mixtures thereof. Examples of inorganic materials incluude vitreous, non-crystalline materials such as glass and vitreous ceramics. Examples of film-forming organic polymers include acrylonitrile/ styrene copolymer, cellulose acetate, cellulose nitrate, ethyl cellulose, methyl cellulose, polyamide, polymethyl methylacrylate, polytriuorochloroethylene, polytetrafluor ethylene, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinyl chloride/ acetate copolymers, polyvinylidene chloride/polyvinyl chloride copolymers, polycarbonates, regenerated cellulose (cellophane) and the like. An especially preferred class of film forming polymers are polyesters such as polyethylene terephthalate.

Associated with one face of the backing member is a layer of radiation-sensitive silver halide emulsion. In general, any conventional silver halide composition can be used in this invention because all are to a greater or lesser extent electron and photon sensitive. By the term radiation as used in this application, reference is had to electro-magnetic energy inclu-ding wave lengths encompassing the X-ray, ultraviolet visible and infrared regions of the spectrum as well as beta-ray radiation, protons, ions, electrons and photons. Naturally it is usually preferred to use silver halide emulsions which have the capacity to form latent images when struck by electron or photon beams of relatively low energy, after a relatively short exposure.

Silver halide compositions after being struck by electrons or photons so as to form a latent image therein are thereafter subjected to known silver halide photographic development procedures during which time selective deposits of silver are formed by in situ reduction. The local concentration of silver in any given area usually corresponds to the quantity and energy of the electrons or photons striking su-ch area, though in the development process one may chemically reverse the location of the silver deposits so that they correspond instead to lightly struck or non-photon or non-electron struck areas.

In general, the silver halide electron beam sensitive compositions useful in constructing media of this invention can be in any convenient physical or chemical form. One convenient form is that of an emulsion. Usually, as

. those skilled in the photographic arts will appreciate, silver halide emulsions comprise a mixture of silver halide grains dispersed in a transparent binder, such as gelatin. A binder is chosen so as not to interfere with latent image formation, so as to permit a uniform dispersion of the silver halide grains therein, and so as to allow developing solutions to permeate the binder and reduce the electronstruck lhalide grains to free silver deposits. The spectral response of the binder should be such as not to appreciably impede photon transmission therethrough at the wave lengths association with the fluorescent materials used, when it is desired to collect the light from the emulsion side of the construction.

A silver halide compositi-on is chosen so as to contain grains of silver halide of sufficiently ne size to permit recording and readout of the information resolution desired.

A silver halide composition is present in a recording medium of the invention usually in the form of a discrete layer positioned relatively near that surface of the medium which is to be exposed to the recording beam. This layer of silver halide material is usually made as thin as praclticable t-o permit easy penetration of the electron beam when excited during readout from that side. However, it is always sufliciently thick to obtain satisfactory masking of the fluorescent layer on readout. Obviously, this is a compromise condition which will vary widely from one medium construction to another, etc., so that it is not possible to give precise numerical limits which will be applicable to all media constructions of the invention. If a medium is used so that a scanning ele-ctron beam must penetrate silver deposits during readout, then a silver halide emulsion layer thickness initially must not be such as to completely impede passage of a readout beam therethrough. In general, it is found that the thickness of a silver halide composition layer in a medium construction will be in the range of from about l to microns.

In general, it is preferred to coat the electron-sensitive silver halide emulsion, as by any conventional coating procedure, upon one face of a recording medium of this invention so as to produce a coating thickness having a uniform silver content which is at least about 500 milligrams per square meter of surface area.

A silver halide composition for use in media of this invention is naturally chosen so as to have physical and chemical characteristics such that when incorporated into a particular medium construction, the medium can function in a high vacuum environment. In addition to freedom from various forms of deterioration, these characteristics should be such that the composition does not interfere with the ability of a medium to be handled, transported, and otherwise manipulated and stored without deterioration or undergoing appreciable deleterious physical transformation. Because the manufacture and formulation of silver halide compositions is well known to those of ordinary skill in the art, no extensive discussion is believed necessary herein.

Typical silver halide compositions useful in constructing media of this invention are described in Photographic Chemistry, vol. I, P. Glafkides, Fountain Press, London, 1958, pages 298-326, under the heading of General Principles of Emulsion Preparation? Although any electron-sensitive silver halide emulsioncan be used, it is preferred to use the so-called slow emulsions because of their characteristic fine grain. In fact, Lippmann emulsions or modified Lippmann emulsions are preferred. Formulations for such emulsions are given in Glafkides, pages 337-368. Although gelatin is a preferred binder for use in preparing silver halide emulsions, media useful in this invention do not require such. @ther binders, such as polyvinyl acetate and polyvinyl pyrrolidine, methyl cellulose, or the like, can be used either partially or fully t replace gelatin. Photographic emulsions utilizing silver chloride, silver bromide, silver iodide and combinations thereof can be and have been used in media useful in this invention.

Fluorescent compositions useful in this invention are, in general, those which are capable of photon emission when struck by excited or accelerated electrons. Fluorescent materials capable of emitting photon energy 1n the range of from about 2,000 to 10,000 A, units are preferred. Y

As those skilled in the art will appreciate, fluorescent compositions are generally very well known. Commonly two classes of yfluorescent compositions are recognized, phosphors and scintillators. Phosphors are commonly inorganic crystalline materials inthe form of fine' grains which, when dispersed in a suitable binder and deposited in layer fashion upon la substrate,y iluoresce when struck with excited electrons. y

Scintillator compositions, on the other hand, generally comprise a solute and a solvent. The solute co-acts with the solvent to cause the whole composition to emit photon energy in response to electron excitation. The solute can actually be a mixture of the two or more materials, one component commonly being called a primary s-olute. and the others the secondary solute, tertiary solute, etc., as the case may be. The secondary or tertiary solute commonly functions to alter or shift the wave lengths associated with the characteristic photon emission for a given Scintillator composition.

Solvents used in the scinti-llator compositions employed in the present invention yare organic polymeric materials capable of existing as stable solids both at ambient temperatures and pressures and under the high vacuu-m conditions characteristically employed during electron beam recording and readout. The solvent comprises up to at least `about 96 weight percent of the total Scintillator composition. The solute is distributed throughout the solvent uniformly on a molecular Ibasis. One common cl-ass of solvent materials includes polymers such as polystyrene, methyl cellulose, and the like which are soluble in organic liquids. Thus, in such cases it is convenient to dissolve both the scintil-lator materials and the polymer materials' in such an -organic liquid and then coatthe resulting liquid mixture in layered fashion to a desired thickness upon a medium construction of the invention. When the organic liquid is evaporated, there remains the scintillator material Idissolved in the polymer. Another common class of solvent -materials comprise melt-extrludable polymers; here the scintillators are dispersed in the molten polymer before the same is extruded and cooled.

Grain-free fluorescent compositions (e.g., scintillator compositions) are generally preferred for use in this invention.

As used in this specification, the term layer has reference to a stratum or thickness of material, e.g., of supporting material, of fluorescent material, -or of conductive material (see below). The term layer also has reference to the fact that, unless otherwise indicated, two or more materia-l components of a medium construction of this invention can be combined into a single stratum lor thickness. Furthermore, respective layers in 4a medium construction of the invention can be in any sequence, unless otherwise indicated.

Thus, in one preferred class of media of this invention, a scintillat-or composition and a backing material are combined into a single layer. Thus scintillator materials are dissolved and uniformly dispersed in backing materials. One especially useful solvent-backing material in such combined construction is polyethylene terephthalate. In general, for purposes of this invention it is preferred to employ as solutes for scintillator compositions substances which are substantially transparent to the photon emission characteristically emitted by the whole scintillator composition when such are excited by electrons.

Fluorescent compositions have associated with them characteristic persistence times by which is meant the period of time following the removal of excitation required for the photon emissi-on to decay to a level approximately one percent -of its value at the time of cessation of excitation. So as to provide high-density, highcapacity, high-speed capabilities in the media of this invention for electron beam recording and readout purposes, persistence times associated with fluorescent compositions useful in this invention should not be longer than about -6 seconds. For example, the P-15 phosphor (zinc oxide type) has a persistence of about one microsecond. Scintillat-or compositions dissolved in appropriate polymer binders have persistence times commonly not more than about 10-8 seconds; for example, that of paraterphenyl is about 10*8 seconds. For best results, the luminescence persistence of a fluorescent layer should have a shorter time duration than the period of the highest readout frequency associated with a given prerecorded mass of information to be read out.

The photon emission capability of a fluorescent cornposition used in a medium of this invention, as measured for example, in terms of lumens per watt, or the like, should, of course, be sufficient to provide a satisfactory signal-to-noise ratio for readout purposes following exposure and development of a medium.

Obviously, depending upon equipment, operating conditions, fidelity desired, etc., selection of photon emission capabilities for a medium construction may be necessary to meet the requirements of a particular use situation within the spirit and scope of this invention.

Since the preparation of fluorescent compositions is well known and does not constitute a part of the present invention, extensive discussion of their preparation and properties is not deemed necessary or desirable here- 1n.

As indicated, storage media of this invention have incorporated therewithin a layer of an electrically conductive material in the form of a continuous film or particulate layer which has a surface resistance less than about 108 ohms per square. Preferably, such layer has a thickness not greater than about 4000 A.

A layer of conductive material is so associated with a medium of the invention as to be able to drain off electrons when grounded. A preferred medium construction employs a layer of conductive material which has a light transmission of at least 20%.

For this purposes of this invention, light transmission through a conductive layer can be measured by means of a Welch Densichron Catalogue No. 2150, manufactured by the W. M. Welch Scientific Company, 1515 Sedgwick Street, Chicago 10, Illionois. This instrument is adjusted to read light transmission on exposure of the light sensing electronic phototube to room lighting. A sample of the material to be measured for light transmission is then placed on the orice of the light sensing probe and a light transmission measurement is made by reading the scale of the meter.

For purposes of this invention, surface resistance in terms of ohms per square is measured by attaching electrodes to opposite sides of a square of the conductive' layer under measurement. The electrodes are part of the resistance measuring instrument. The measured resistance of the square is independent of the size of the square. In measuring the surface resistance of the conductive layer in this media, care must be exercised that contact is made with the conductive layer and not with any other layer as these other layers are essentially insulating.

It is preferred to use a layer of conductive material not thicker than about 0.001 mil. Thus, it is convenient to deposit a conductive material upon the face of a medium being constructed either by conventional vacuum vapor deposition or by conventional electrolytic deposition. However, when one employs as a backing material a conductive substance such as a metal foil, it is convenient and very practical to simply layer fluorescent material and silver halide emulsion over such metal sheetlike member. Thus, the layer of silver halide emulsion constitutes one face of such a medium construction, the me-tal the other face, with a layer of fluorescent composition in between.

Suitable conductive materials for use in forming conductive layers for use in media of this invention include metals such -as aluminum, silver, copper, and the like. Sometimes an organic particulate conductive material such as carbon particles can be used in the construction of a conductive layer by loading (i.e., admixing such particles with) an organic polymeric film forming material to an extent sufficient to render a lilm formed therefrom conductive to the desired extent. When a layer of conductive material is positioned between a layer of silver halide material and a layer of fluorescent composition, the l-ayer of conductive material must be capable of transmitting at least 20% of the photon energy transmitted by the scintillator composition when it is electron excited.

In media of -this invention, the layer of fluorescent composition is preferably chosen and prepared so as to be capable when in layer form in a medium construction of uniformly emitting photon energy (or light) in response to uniform electron excitation. Similarly, the layer of conductive material when incorporated into a medium construction of the invention is preferably chosen as to be capable of uniformly conducting electrons. If a backing layer is to be capable of passing excited electrons and/or photon energy, then su-ch backing should be uniformly transmissive of, respectively, the photon energy or such excited electrons or both as the case may be. Similarly, the layer of silver halide emulsion should be preferably so chosen that when it is coated as a layer in a medium construction of the invention it is capable of producing, as a result of an exposure to a modulated, scanning electron beam, a scanning photon beam, or a photon image :and a subsequent developing operation, a masking layer which accurately and even uniquely shows variations in the intensities of the somodulated electron beams striking such emulsion layer during each exposure.

Media of this invention can be prepared by a convenient procedure. For example, one procedure to begin with is a preformed backing member. Then, one face of such backing can be coated with `a conductive layer. Next, such coated face or the opposed face can be coated with a layer of scintillator composition, if the 'backing does not already contain incorporated therein a scintillator material. Finally, the resulting intermediate constructi-on is coated on one of its faces with :a layer of silver halide emulsion, e.g. silver chloride, silver bromide-chloride, or silver bromoiodide so as to produce a desired coating weight of at least about 500 milligrams of silver per square meter of surface area. Conventional coating techniques can be employed with intervening drying steps between successive coating operations.

Usually the silver halide layer is kept distinct from the other layers in a medium construction though the other layers are placed next to one another in any sequence. In fact, any combination of the backing material, the fluorescent material and the conductive material can be effected provided one or more of these components can be functionally admixed together so as to provide at least a single layer thereof. In general, each of the other layers other than the silver halide emulsion layer are on the same side of the silver halide emulsion layer. Preferred medium constructions are flexible and thin so as to have total thicknesses of the same order of magnitude commonly -associated with conventional photographic films and magnetic tapes so as to permit the use of conventional tape transport mechanisms and handling procedures generally.

While adjoining layers need bear no special relationship to one another, it will be appreciated that the silver halide emulsion layer should be so located in relationship to the exterior surface of a given medium as to facilitate development of that medium'following exposure thereof to a modulated electron beam. Before coating a silver halide emulsion upon one surface of a medium of the invention, one can coat such surface with a substratum or subbing layer to facilitate and promote the adherence of the emulsion to the base surface. Subbing formulations and methods for their use are well known to those skilled in the art. Typical subbing formulations are given for example, in P. Glafkides, Photographic Chemistry, vol. I, pages 467-69; U.S. Patent No. 2,341,877, British Pat. No. 552,085, Brit. Pat. No. 545,905, and Belgium Pat. No. 617,581.

Any one or more layers may be positioned between the silver-halide layer and the fluorescent layer. Each such intervening layer is capable of transmitting at least 20% of the photon energy emitted by the fluorescent layer When excited.

Occasionally, it is desirable to coat a silver halide emulsion layer in a medium construction of the invention with `a protective layer or anti-abrasion layer which does not interfere with the development ofthe emulsion following exposure of same to an electron beam. Such layers are commonly used on photographic emulsions to facilitate handling and are well known to those skilled in the art. AOne useful protective layer, for example, which we have found to be useful, is given in P. Glafkides, Photographic Chemistry, vol. I, page 474.

One preferred recording medium construction of this invention integrally comprises la layer of radiation-sensitive silver halide emulsion, a layer of fluorescent composition capable of emitting photon energy when excited by impinging electrons, a layer of electrically conductive material and a layer of supporting material. The silverV halide layer is distinct from the other layers, land each ofthe other layers'is on the same side of theA silver halide layer and in any sequence. When the conductive layer is positioned betweenv the silver halide layer and the fluorescent layer, it is capable of transmitting at least 20% of the photon energy emitted by the fluorescent layer when electron excited.

A still more preferred construction is similar to that just described except that the silver halide layer has a uniformsilver content of at least about 50 milligrams per square meter of surface area; the fluorescent layer is characterized by having a persistance ltime not longer than about 106 seconds and average individual grain sizes less than about 1 micron in maximum dimension; and the conductive layer has a surface resistance less than about 10a ohms per square. In such constructions, the fluorescent layer most preferably comprises a grain-free scintillator composition.

It will be appreciated that ina medium construction of this invention, the total thickness of, and the inter-relation between layers therein is such that:

(a) The silver halide layer is adapted to form a latent image upon exposure to a preselected radiant energy pattern,

(b) The silver halide layer is further adapted to be chemically developed following exposure to said pre-selected radiant energy pattern so as to produce a plurality of deposits of silver grains therein in a pattern corresponding to said preselected radiant energy pattern, and

(c) The fluorescent layer is adapted 'to emit photon energy when one face of a medium is bombarded by elec- -trons of predetermined minimum average energy.

Characteristic properties of media of this invention depend not only upon the nature of the starting materials but also on the manner in which a particular medium construction is assembled, aside from recording and development conditions. For example, one of the significant characteristics of a medium construction is its socalled signal-to-noise ratio. This ratio for a particular medium is affected of course by a medium construction, by the equipment used, development procedure, the nature of the information being recorded and read out, and other factors. As respects the medium itself, however, the silver halide emulsion signal-to-noise capability is largely a function of the structure of the developed recorded image. In turn, this image-wise pattern is dependent upon such factors as grain size, granularity, turbidity, resolving power, sharpness, etc. See, for example the discussion by C. E. Mees in his book The Theory of the Photographic Process, Macmillan Company, New York, revised edition, 2nd printing, 1959, Ch. 24.

Each of these properties may he influenced by varying such emulsion characteristics as grain size distribution, silver content, silver to binder ratio, binder composition, the coating thickness and various additives used to influence the structure of the developed image, etc. All these variations are well known in the photographic art; see for example, the detailed account of emulsion preparation in P. Glafkides, Photographic Chemistry, vol. I, pp. 269-418.

Other factors affecting the nature and properties of a medium of the invention are thickness of the scintillator layer, spacing distance (if any) between the scintillator layer and the silver halide emulsion layer, position of the conductive layer in relation to the silver halide emulsion and the scintillator layer, respective layer thickness, light transmission characteristics of the whole sandwich comprising a given medium construction, and the like.

Those familiar with conventional photographic technology will lappreciate that the type of development used can have strong effects on graininess, contrast, image sharpness, covering power and the like. The processing of silver halide emulsions is described, for example, in P. Gl-afkides, Photographic Chemistry, vol. I, pages 48-188.

An especially preferred class of media within the teachings of the present invention is one capable of recording information in a high density manner, that is to say, ca-

pabale of recording information at a bit density greater than about 105 bits of inform-ation per square centimeter of surface area. Such media employ both grain-free fluorescent materials and grain-free backing materials. If the backing material and the fluorescent material are not grain-free then it is difficult and even commonly impossible to obtain high signal-to-noise ratios on readout of such high density recorded information. The term high as used in reference to signal-to-noise ratios refers to ratios exceeding about 7:1 and preferably exceeding about 10:1.

Referring to the figures, it is seen that FIGURES 1 and 4 show four-layer constructions while FIGURES 2, 3 and 5 show three-layer constructions. Captions designate the identifica-tion of individual layers in each construction shown.

FIGURES 6 and 7 show the appearance of media constructions after such have been subjected to recording and development. Similarly, FIGURE 7 shows the appearance of a medium such as that shown in FIGURE 4 after recording and development. In these figures the developed silver halide emulsion is referred to as a masking layer. The dark blocks in this masking layer designate silver deposits produced in radiation-struck areas during the development process.

Media which are partially light transparent provide the capability of reading out by unmodulated electron beam bombardment through the backing layer so as to excite the scintillator composition in a medium construction to emit photon energy uniformly without having to excite such composition by electron beam bombardment against or through the masking layer.

To record or store information with an electr-on beam using a medium of the invention, one can position a medium construction typically perpendicularly across the path of an electron beam in an evacuated environment. The beam can 'be intensity modulated with input information to be recorded (stored). The so modulated beam is caused to scan a surface of such storage medium so as to selectively alter the silver halide emulsion composition of such medium in a manner representative of the modulation associated with the scanning beam. Alternatively, information can be recorded by conventional photographic exposure jrocedures or 'by a modulated light beam such as produced by a Laser.

Thereafter, the so-recorded medium is subjected to development so as to convert the silver halide emulsion into an image-wise pattern of silver deposits and produce a masking layer, such silver deposits being uniquely representative of the information being recorded.

To read out or retrieve the recorded information from a recorded and developed medium, one positions such medium in an evacuated environment and exposes one surface of such medium to electron excitation (usually a scanning electron beam) so as to produce differential photon emission from one surface of the medium. The term photon emission or equivalent as used herein has reference to not only visible light but also that energy adjoining in the ultraviolet and infrared portions of the spectrum. Although the layer of fluorescent material is thus excited by such electron excitation, such resulting photon emission is screened or selectively filtered as it passes through the masking layer so that there results from that surface of the medium bearing the masking layer a differential photon emission which is representative of the originally recorded information. The differential photon emission can :be detect-ed optically or electronically.

The invention is further simplified by the following specific illustrative examples.

In each of the following examples the supporting layer has a surface roughness not greater than about 1.5 micro inches as measured on the Micro Surf model 180 and a serviceable temperature range from about -20 C. to 100 C.

Example I A flexible transparent film of cellulose acetate (sold under the Kodapak trademark by Cellulose Products Division, Eastman Kodak Company, Rochester 4, New York) 5 mils thick is vapor coated with aluminum to provide a conductive layer of albout 60 A. in thickness and an electrical resistance of about 2000 ohms per square. Film light transmission after vapor coating is 45%. The Ibacking is then slit to 16 mm. width and perforated for fuse in the conventional type of sprocket-drive transport.

The aluminized surface is provided with a light transparent fluorescent coating in the fol-lowing manner:

To 18.75 grams of toluene is added with stirring 0.175 gram of para-terphenyl (highest purity) and 25 grams of a 30% toluene solution of a butadiene-styrene copolymer (sold under the trademark Pliolite S7 by Goodyear Tire and Rubber Company, Chemical Division).

This coating solution is then knife-coated by means of a knife-over-roll coating apparatus upon the surface of the 16 mm. wide perforated backing. A 2 mil orifice is employed for the knife setting which results in a dried coating thickness of 0.15 mil. The coating is air oven dried at 200 F. for 10 minutes.

To provide acceptable adhesion of a silver halide emulsion coating to the resulting coating, the following subhing solution is applied Ias an extremely thin coating by passing the coated side lightly against a saturated sponge containing the subbing solution. This subbing solution is prepared in accordance with the teachings of Belgium Patent 617,581, and contains 2.5 g. gelatin (photographic grade) in 10 milliliters (ml.) water and 5 ml. of a 25% by weight solution of salicylic acid in methanol diluted with 245 ml. methanol and ml. acetone. The so-applied sulbibing coating is allowed to air dry. The so sulbbed coating is now overcoated with a silver halide emulsion in the following manner:

A silver halide emulsion is prepared as described in Glafkides Photographic Chemistry, vol. I, pages 341-353.

The resulting silver emulsion contains 19.01% solids consisting of 12% gelatin and an 80:20 Weight ratio of silver chloride to silver bromide. To the above emulsion is added with stirring 10 parts of a 5% aqueous solution of saponin. Saponin, as those skilled in the art will appreciate, is still the most widely used wetting agent for emulsion coating although it has only moderate surface active power. It is a natural product of uncertain chemical constitution, and its activity varies with its source, which must Ibe carefully controlled. The sources are still quillaja bark, horsechestnuts land soapwort root. It is available from J. T. Baker C-hemical Company and A. K. Peters Company.

Then in a ydark room provided with red photographictype illumination and using the same coating apparatus described above with a knife setting for the hopper type knife of 2.0 mils, this silver halide emulsion is coated at a temperature of 50 C. The resulting coating after air drying is found to be about 0.3 mil (7.5 microns) in 'thickness. The amount of silver in the dried coating is about 2000 mg. per square meter of surface area.

This medium is now used under photographic dark room lighting conditions for electron beam recording and read out as follows: The medium is mounted into a 16 mm motor driven sprocket driven tape transport mechanism and guided under an electron beam in a vacuum chamber under a vacuum of about 5 104 mm. Hg. The axis of rotation of the sprocket is parallel to the direction of deflection of the electron beam so that the plane of film movement is effectively perpendicular to the direction of deflection. Film or tape speed is about 9 inches per second.

A conventional television-type horizontal deflection is used to deflect the electron beam. The horizontal deflection is accomplished by driving the deflection coil on the electron gun with a 15,750 cycles per second sawdeflection.

tooth current. The sawtooth has a scan period of about 53.5 microseconds and a retrace period of about 10 microseconds. The resultant horizontal deflection of the electron beam is set for about 1 cm. width at the surface of the media.

The electron beam is about 10 microns in diameter at the surface of the media and has an acceleration of about 15 kilovolts. The beam current is intensity modulated by applying a modulating voltage at the electron gun grid. The intensity modulation of the beam corresponds to the information to be recorded. The peak beam current under such modulation is about 0.1 microampere.

The media and electron gun are mounted in a vacuum chamber held at about 5 104 mm. Hg pressure.

The recording takes place by simultaneously moving the film or tape and deflecting and modulatingthe electron beam so that a scanned line-like latent image pattern of the information results.

After recording and removal from the vacuum, the exposed sensitive layer is developed in a developer ysolution for about two minutes at about 68 F. whose composition is as follows:

Water cc 500 p-Methylaminophenol sulfate gra-ms" 2.2 Sodium sulfite do 96.0 Hydroquinone do 8.8 Sodium carbonate, monohydrated do 56.0 Potassium bromide do 5.0

Add cold water to make 1.0 liter.

An equivalent developer is commercially available as Kodak D19 developer manufactured by Eastman Kodak Company. After development the media is rinsed in water at about 68 F. for about 30 seconds and transferred to a fixing bath at about 68 F. for about 2 minutes. Composition of the fixing bath is as follows:

Water (125 F., at time of mixing) cc-- 600 Sodium thiosulfate (hypo) gms 240.0 Sodium sulfite, desiccated gms-- 15.0 Acetic acid, 28% pure cc-- 48.0 Boric acid, crystals gms 7.5 Potassium alum. (aluminum potassium sulfate) gms-- 15.0

Add cold water to make 1.0 liter.

An equivalent fixer is commercially available as Kodak Fixer for Films, Plates and Papers as manufactured by Eastman Kodak Company.

After fixing, the media is washed in water at about 68 F., for about five minutes. The media is then removed and allowed to dry.

For retrieval (readout) of the recorded information, the processed film or tape -media is repositioned in the vacuum chamber for the record and readout apparatus and mounted for the same media movement. Beam defiection conditions remain the same as during the recording.

The electron beam is accelerated to about 20 kv. and the diameter of the electron beam is maintained about microns. The beam current is kept constant during Alternatively it may be shut off during the retrace period. The beam -current during scanning is about 0.5 microampere.

To detect the fluorescence from the media where the electron beam strikes the media, an RCA photomultiplier type 1P28 is mounted in close proximity to the film or tape media area `of fiuorescence.

The readout takes place by simultaneously moving the media and defiecting the electron beam in the same manner as done in recording. The fluorescence of the area under the beam is detected by the photomultiplier which converts the fiuorescence to an electrical signal output which is a reproduction of the original recording signal. Excellent quality reproduction is obtained with high sig- -nal-to-noise ratio.

Example II With polyethylene terephthalate resin granules (manufactured by the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota) is uniformly mixed 1% by weight of paraterphenyl (high purity). The mixture is dry-blended and extruded by conventional film forming procedures so as to produce a transparent film having a hygroscopic coefficient of expansion of about 1 l0"5 inch per inch per percent relative humidity, a thermal coefficient of expansion of about 15x106 inches per inch per degree Fahrenheit, land a surface roughness not greater than about 1.5 microinch. In this construction the backing material and the fluorescent layer material are thus combined into a single layer of 4 mil thickness.

The resulting film is then vacuum vapor coated on o-ne surface by vacuum Vapor deposition with a layer of aluminum metal to yield about a 45% light transmissive film which has an electrical resistance value for the aluminum coated surface of about 2000 ohms per square.

The resulting aluminum vapor coated surface is then subbed with a very thin coating applied from a solution to achieve adhesion of the photographic emulsion. Such subbing solution is prepared in acccordance with the teachings described for-the preparation of subbing solutions in P. Glafkides, Photographic Chemistry, vol. I, pages 467-69. The resulting subbed aluminized surface of the film strip in a 16 mm. Width is then stripecoated with a layer of silver halide emulsion.

A silver halide emulsion is prepared as described in P. Glafkides Photographic Chemistry, vol. l, pages 341- 353. The resulting silver emulsion contains 19.01% solids consisting of 12% gelatin and an 80:20 weight ratio of silver chloride to silver bromide. To this emulsion is added l0 parts of a 5% aqueous solution of saponin (as defined in Example I above).

Then in a dark room provided with red photographictype illumination and using the same coating apparatus described above with a knife setting for the hopper type knife of 1.0 mil, this silver halide emulsion is coated at a temperature of 50 C. The resulting coating after air drying is 4found to Ibe about 2 microns in thickness. The amount of silver in the dried coating is about 530 mg. per square meter Iof surface area.

The resulting construction constitutes an electron beam recording medium of this invention.

The medium is used in an electron beam recording development and readout operation under conditions identical to those described in Example I above. Excellent fide-lity of reproduction of the recorded information is observed.

Example III A flexible transparent film of polyethylene terephtha- Ilate (available as Type A, 500 gauge, Mylar from E. I. `du Pont de Nemours and Company of Wilmington, Delaware) is vapor coated with aluminum to provide a conductive layer approximately 1000 A. in thickness, having a resistance of about 0.8 ohm per square. The backing is slit and perforated to rolls 16 mm. in width for use in `sprocket-drive transport equipment. VThe aluminized surface of the tape is provided with a fiuorescent coating as follows:

A dispersion containing a 4:1 ratio of zinc oxide to polymeric binder is prepared in the following manner: toa porcelain ball mill loaded with one-half inch porcelain balls, as the grind media, are added 200 grams zinc oxide, analytica-l reagent grade (Ma-llnckrodt Chemical Works, St. Louis 7, Missouri). 50 grams of Pliolite-VT (a trademark for a copolymer of 88:12 ratio of vinyl- `toluene and butadiene, a product supplied by the Chemical Divisi-on of the Goodyear Tire and Rubber Company, Inc., Akron 16, Ohio) and 350 grams of ya one to one mixture by volume of acetone and toluene are added. After ball-milling the above mixture for 24 hours, the ball mil-l is opened and to the mill is added a mixture consisting of 4 grams -of Lecithin, supplied by the Central Soya Company, Inc., Chemurgy Division, Chicago 39, Illinois, and 116 grams of one to one by volume of acetone and toluene. The ball mill is closed and milling continued for an additional one hour. The final solids of the dispersion is 35.4% containing a weight ratio of 4:1 zinc oxide to Pliolite-VT.

The resulting dispersion is then coated onto the aluminized surface of the 16 mm. wide flexible backing, described above, by means of a stripe coating apparatus consisting of a hopper type knife set over .a steel roll and equipped with undercut guide rolls. Using a knife or orifice of about 2 mils, the dispersion described above when coated onto the 16 mm. wide, perforated backing gives a uniform smooth coating which after 200 F. air oven drying for minutes is found to be in the 0.15 mil range in thickness.

To provide a light and/or electron beam sensitive coating, the zinc oxide/Pliolite-VT coated, 16 mm. backing, described above, is overcoated with a silver halide/ gelatin emulsion in the following manner: In a dark room provided with red lights, employing the samecoating" consisting of 12% gelatin, andan 80:20 weight ratio of silver chloride to silver bromide. The preparation of the silver halide emulsion is in accordance with the principles described in Chapter 18, Photographic Chemistry, vol. I, P. Glafkides, published by Fountain Press Publications, London, 1958. Immediately before coating to the heated silver halide emulsion, is added with stirring ,Y

10 parts of a 5% aqueous solution of saponin (see above in Example I), a glucoside type of emulsifying agent. The so-coated silver halide/ gelatin coating on air drying is Vfound to be 0.3 mil (7.5 microns) in thickness.

The resulting construction constitutes an electron beam recording medium of this invention. l

The medium is Iused in an electron beam recording development and readout operation under conditions identical to those `described in Example I above. Excellent fidelity of reproduction of the recorded information is observed.

Example 1V A flexible transparent film of polyethylene terephthalate (available as Type A, 500 gauge Mylar from E. I. du Pont de Nemours and Company of Wilmington, Delaware) is vapor coated with aluminum to provide a conductive layer approximately 1000 A. in thickness having a resistance of about 0.8 ohm per square. The backing is s-lit and perforated to provide 16 mm. width rol-ls for use in sprocket drive transport equipment.

To provide the fiuorescent coating composition, a dspersion of 4:1 weight ratio of zinc oxide to binder is prepared in the following manner: 137 grams of zinc oxide (St. .loe No. 920, suppled by the St. Joseph Lead Company, New York 17, New York) are added to 114 grams of a 30% by weight solution 'of Pliolite S7 (a trademark for the copolymer of 70:30 butadiene/ styrene as supplied by the Chemical Division of the Goodyear Tire and Rubber Company, Inc., Akron 16, Ohio). To this is added a solution consisting of 262 grams of toluene and 2.7 grams of lecithin (supplied by the Central Soya Company, Inc., Chemurgy Division, Chicago 39, Illinois). The 33.8% solids mixture is ground for 24 hoursin a porcelain ball mill using one-half inch porcelain balls.

The resulting dispersion is found to be satisfactory for knife coating on the aluminum surface of the vapor coated film. The coating procedure involves the use of the hopper knife over roll coating apparatus. A 2 mil orilice of the knife setting gives a 0.3 mi-l thick coating after air oven drying for 10 minutes at 200 P. The resulting coating is smooth and uniform in appearance.

The surface of the zinc oxide coa-ting is then coated with the silver halide emulsion in the manner described in Example II above to provide a uniform silver halide/ gelatin coating of about 2 microns in thickness containing about 500 mg. of silver per square meter.

The resulting construction constitutes an electron beam recording ymedium of this invention.

The medium is used in an electron beam recording development and readout operation under conditions identical to those described in Example I above. Excellent fidelity of repreduction of the recorded information is observed.

Y Examples V-XIV These media employ scintillator compositions as the fluorescent material. v

The backing film layers are as shown below respectively in Tables I, IIl and III. In these tables, the 5 mil polyester film is available from the E. I. du Pont de Nemours and Company, as Type A, 500 gauge Mylar film, the 3 mil polyester film is available from the E. I. du Pont de Nemours and Company as Type D, 300 gauge Mylar film, and the 5 mil acetate film is available from Eastman Kodak Company as a celluloselacetate type film called Kodapak 4.

In each case, with the exception of the control, the backing is vapor coated under vacuum with aluminum to an extent sufiicientto allow light transmission of about 45% (the electrical resistance Value of such a coating is about 2000 ohms per square).

The control is a 5 mil polyester lilm first vapor coated lwith an opaque layer of aluminum having a resistance value ofl vabout 0.8 ohm vper lsquare 'and the/n overcoated with a 0.3 mil coating of zinc oxide in a 70:30 styrenebutadiene copolymer (available as Pliolite S7 as sold by the Goodyear Tire and Rubber Company) using a zinc oxide to binder ratio of about 4i l.

In Table I below are l-isted various 4organic uorescing materials each of which is first dissolved in a solution of Pliolite S7 in toluene and then coated onto a 5 mil cellulose acetate backing. The dried samples are exposed to an electron beam accelerated by a potential of 20 kilovolts (kv;) and having a current of 3.0 microamperes under a vacuum of 5x104 mm. Hg. The light output is detected and measured by means of an RCA Type 6199 photomultiplier using a plate voltage of 500 volts.

In 'Table II are shown the relative light emission data for two scintillator coatings applied by the stripe coating technique from solutions prepared by dispersing 0.11 gram of the fluorescing agent in 2.0 grams of methyl ethyl ketone followed by dissolving in a 25 gram methyl ethyl ketone solution containing 20% solids of cellulose acetate b-utyrate polymer (supplied as EAB-38h20 by the Eastman Chemical Company).

The dried samples are exposed to an electron beam under the same conditions described above for Table I, and the light output is detected and measured using the 500 volt plate voltage on the photomultiplier, as in Table I above, and the associated amplifying equipment.

In Table III are listed various coating compositions which exhibit iiuorescence or photon emission when excited by the electron beam. The organic fluorescing la gent either by itself or as a mixture with a second additive is dissolved in a toluene solution of Pliolite S7 and then coated onto the aluminized surface of the film backing. The dried samples a-re exposed fto an electron beam accelerated by a potential of 20 kilovolts and having a current of 0.5 microampere under a vacuum of about 5x10-4 mm. mercury. The light output is detected by means of an RCA Type 6199 photomultiplier'using a plate voltage of 360 volts.

TABLE I.-LIGHT EMISSION OF ORGANIC FLUORESCENT COATINGS ON ALUMINUM VAPOR COATED FILM BACKINGS Phosphor or Example Scintillator, Relative No. Film Backing lolymer Binder Phosphor or Scintillator Parts by wt./ Light Out- 100 Parts of put 1 Binder Control.... 5 mil Mylar.. Pliolite S-7 Zinc oxide 2 400 100 1 5 mil acetate d Naphthalene.. 0. 5 12 {Anthracene 0. 5 73 Naphthalene 2. 5 Para-quaterphenyl. 0. 4 100 2, 5-diphenyloxazole. 2. 0 135 Para-terphenyl 2. 120 {Para-terphenyl l. 45 54 2, -dipl'ienyloxazole. 0. 3 `{Anthmoene 1. 75 4 2, -diphenyloxazole. 1. 75 Anthracene 1. 0 77 1 RCA type 6199 photomultiplier was used with a 500 volt plate supply. microamp beam current was allowed to raster scan the scintillator coating.

2 St. J oe, No. 920 zinc oxide, St. Joseph Lead Company.

A kv. electron beam with a 3 TABLE II.LIGHT EMISSION OF ORGANIC FLUORESCENT COATINGS ON ALUMINUM VAPOR COATED FILM BACKIN GS Phosphor or Example Seintillator, Relative No. Film Backing Polymer Binder Phosphor or Scintillator Parts by \vt./ Light Out- 100 Parts of put l Binder Control 5 mil Mylar Pliolite S-7 Zinc oxide 3 400 100 9 3.0 mil polyester... Cellulose Acetate 2, 5-Diphenyloxazole 2.2 71

Butyrate 2 10 .do do 2 Paraterphenyl 2. 2 37 1 RCA type 6199 photomultiplier was used with a 500 volt plate supply. A 20 kv. electron beam with a 3 mieroamp beam current was allowed to raster sean the scintillator coating.

l EAB, 381, 20, Eastman Products, Inc., Kingsport, Tennessee.

3 St. I oe No. 920 Zinc oxide, St. Joseph Lead Co.

TABLE IIL-LIGHT EMISSION OF ORGANIC FLUORESCENT COA'IINGSl ON ALUMINUM VAPOR COATED FILM BACKINGS 1 All organic sclntillator materials were dissolved in a tolune solution of Pliolite S-7.

7 RCA type 6199 photomultiplier was employed with a plate supply oi 360 volts. A 20 kv. electron beam with a current of 0.5 microarnp was allowed to raster scan the seintillator coating. The relative light output data was calculated on the basis of a value of 100 assigned to zinc oxide coated control.

3 Dimetliyl POPOP =1, 4 bis [2-(L1-methyl--phenyloxazoly)l benzene.

in Example II.

The surface of each fluorescent coating in these examples is first `treated with a subbing solution prepared in accord-ance with the principles described in P. Glafkides, Photographic Chemistry, vol. I, pages 467-69.

The surfaceV of each scintillator coating in these examples is then coating with a silver halide emulsion in the manner described in Example II above to provide a uniform silver halide/ gelatin coating of about 2 microns 60 in thickness containing not less than about 500 mg. of silver per square meter.

The resulting constru-ctions each constitute an electron beam recording medium of this invention.

Each medium is used in an electron beam recording development and readout operation under conditions identical to those described in Example I above. Differential photon emission is observed representative of the initially recorded information.

The subbed surface of the lm is now coated with a silver halide emulsion described in Example II using the procedures therein described. The zinc oxide coating is prepared. in the following manner:

To 40 grams of an aqueous solution containing 5% Iby Weight of gelatin are added 30 Igrams of an aqueous dispersion of zinc oxide (American Zinc Company, Type ZZZ-66l). The zinc oxide dispersion is prepared by grinding in a Iball mill a mixture of parts zinc oxide, 1.5 parts potassium tripolyphosp-hate, 2 parts polyacrylamide (supplied as Cyanimer P-250 by American Cyanimid Company) and parts of Water.

The resulting mixture of the above zinc oxide dispersion and the gelatin solution are employed to provide a thin coating of about 0.1 mil in thickness over the photographic silver halide emulsion. The coating of the zinc oxide/gelatin layer is performed on a hopper type knife Iover roll stripe coating equipment using a 16 mm. wide perforated construction of the above-described photographic lm.

The air-dried zinc oxide/gelatin coated photographic iilm is exposed to the electron beam at a voltage of 15 Example XVI A flexible transparent film of polyethyleneterephthalate available as Type A, 500Vgauge Mylar from E. I. du Pont de Nemours and Company, Wilmington, Delaware, is vapor coated'with aluminum to provide a conductive layer approximately 1000 A. in thickness having a resistance of about 0.8 ohm per square. This layer is then coated with ay suitable subbing solution to provide adhesion of the subsequent silver halide/barium sulfate coat-ing. This subbing is done as described in Example II above.

The photographic silver bromochloride emulsion contains 7.5% silver, the silver to gela-tin ratio is about 1:1, and the bromide to chloride ratio is about 15:85. The emulsion is prepared according to procedures described in P. Glafkides, vol. I, pages 298-368.

This so-prepared backing is now coated under dark room conditions on a conventional coating machine and photographic emulsions with a layer lmade Iup of an admixture of-2 parts of a barium sulfate dispersion and l part of the photographic silver halide emulsion. The layer after drying is about 6 microns thick, and has a silver content of about grams per square meter and a barium sulfate content of about 5 grams per square meter.

The barium sulfate or 'baryta dispersion is prepared Iby interaction of a barium chloride solution with a sodium sulfate solution in 4the presence of |gelatin as a protective colloid. Formulations for baryta dispersions of this kind are given in P. Glafkides, Photographic Chemistry, vol. I, pages 445-446, and in Report #C 9- 939 of the British Intelligence Subcommittee on the German Photographic Industry. The dispersion contains 30% barium sulfate by weight. l

This medium is now used for electron -beam recording and readout as described in Example I. Differential photon emission is observed representative of the initially recorded information.

Example XVII A 16 mm. wide roll of perforated 5 mil transparent polyethylene terephthalate film is coatedv with a l Imil thick layer of paraterphenyl as taught in Example V.

The paraterphenyl layer is coated with a silver halide emulsion layer according to Example I.

The resulting film is then mounted with the silver halide emulsion exposed in an enclosed chamber, in the manner generally taught by the Schladitz U.S. Pat. No. 2,698,812 to deposit a layer of nickel metal upon the surface of the silver halide emulsion. This layer is estimated to be less than about 250 A. in units in thickness and to have a conductivity of the order of about 106 ohms per square.

The resulting construction is a recording medium of this invention. v

The medium is now used for electron beam recording and readout as described in Example I. Differential photon emission is observed representative of the initially recorded information.

Having described our invention, we claim:

l1.A recording medium capable of emitting photon energy differentially from one face thereof inV response to bombardment of one face thereof with excited electrons following first exposure of one face thereof'tofa radiant energy pattern and then development of the soexposed face to produce a selective radiant energy ma-sk corresponding to such modulation, said medium integrally comprising in combination:

(a) a discrete undeveloped silver halide layer comprising a radiation sensitive silver halide emulsion;

(b) a fluorescent layer comprising a fluorescent composition capable of photon energy emission when excited by impinging electrons;

(c) a conductive layer comprising an electrically conductive material;`

(d) a supporting layer comprising a grain-free supporting material;

(e) when any one of said other layers is positioned between said silver halide layer and said fluorescent layer, such layer is capable of transmitting at least 20% of the photon energy emitted by said fluorescent layer when electron excited;

the total thickness of, and the interrelationship between said layers` in, a said medium being such that (f) said silver halide layeris adapted to form a latent image upon exposure to a preselected radiant energy pattern;

(g) said silver halide layer is further adapted to be chemically developed as part of said medium following exposure to said preselected radiant energy pattern; and

(h) said fluorescent layer is adapted lto -emit photon energy when one face of a said medium is bombarded by electrons of pre-determined minimum average energy.

2. The medium of claim 1 'wherein said silver halide layer and a said fluorescent layer are adjacent one another.

3. The medium of claim 1 wherein a discrete said conductive layer is positioned between said silver halide layer and a said fluorescent layer.

4. The medium of claim 1 wherein a said supporting layer is positioned between said silver halide layer and a discrete said conductive layer.

S. The medium of claim 1 wherein a discrete said conductive layer is adjacent a said fluores-cent layer.

6. A recording medium capable of emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons following first exposure of one face thereof to a radiant energy pattern and then development of the s0- exposed face to produce a selective radiant energy mask corresponding to such modulation, said medium integrally comprising in combination:

(a) a discrete undeveloped silver halide layer compris.

ing a radiation sensitive silver halide emulsion having a uniform silver content of at least about 500 milligrams per square meter of surface area;

(b) a fluorescent layer (1) comprising a fluorescent composition capable of photon energy emission when excited by impinging electr-ons,

(2) characterized by having a pe-rsistence time not longer than about 10-6 seconds, and

(3) further characterized by having, when particulate in nature, average individual grain sizes le-ss than about 1 micron in maximum dimension;

(c) a conductive layer comprising an electrically con'- ductive material having a surface resistance less than about 108 ohms per square;

(d) a supporting layer comprising a grain-free supporting material;

(e) when any one of said other layers is positioned between said silver halide layer and said fluorescent layer, lsuch layer is ca-pable of transmitting at least 20% of the photon energy emitted by said fluorescent layer when electron excited;

the total thickness of, and the interrelationship b etween said layers in, a said medium being such that (f) said silver halide layer is adapted to form a latent image upon exposure to a preselected radiant energy pattern;

(g) said silver halide layer is further adapted to be chemically developed as part of said medium following exposure to said preselected radiant energy pattern; `and (h) said fluorescent layer is adapted to emit photon energy when one face of a said medium is bombarded by electrons of predetermined minimum average energy.

7. A recording medium capable-of emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons following rst exposure of one face thereof to a radiant energy pattern and then development of the so-exposed face to produce a selective radiant energy mask corresponding to such modulation, said medium integrally comprising in combination:

(a) a discrete undeveloped silver halide layer comprising a radiation sensitive silver halide emulsion having a uniform silver content of at least about 500 milligrams per squa-re meter of surface area;

(b) .a fluorescent layer i (1) comprising a fluorescent composition capable of photon energy emission when excited by impinging electrons, l v y (2) characterized by having a persistence time not longer than about -6 seconds, and

(3) further cha-racterized by having, when particulate in nature, average individual grain sizes less than about l micron in maximum dimension;

, (c) a conductive layer comprising an electrically conductive material having a surface resistance lessthan about l08 ohms per square; v .Y y

(d) a supporting layer comprising a grain-free supporting layer; v

(e) said silver halide layer being distinct lfromsai other layers;

(f) when any one of said other layers is positioned between said silverhalide layer and said fluorescent layer, such layer is capable of transmittingat least 20% of the photon energy emitted by said fluorescent layer when electron excited;

' the total thickness of, and the linterrelationship between said layers in,`a said Imedium being such that f (g) said s ilverhalide layer'is adapted to form a Vlaten image upon exposure to a preselected radiant' energy pattern; (h) said silver halide layer is further adapted to be chemically developed as part of said medium following exposure to said" preselected radiant lenergy pattern; and y l Y (i) said fluorescent layer is'adapted to emit photon energy when one face of a saidmedium is bombarded by electrons -of predetermined minimum average energy.

S. A medium as described in claim 7 bearing recorded information therein ywhich silver Vis present in the silver halide layer in the form of a pattern.

9. A recording medium capable of emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons following Vfirst exposure of one face thereof to modulated radiant energy and then development of the sro-exposed face to produce a selective photon energy mask corresponding to such modulation, said medium integrally comprising in combination:

(a) ya discrete undeveloped silver halide layer comprising a radiation sensitive silver halide emulsion having (e) when any one of said other layers is positioned between said silver halide layer and said fluoroescent layer, such layer is capable of transmitting at least of the photon energy emitted by said fluoroscent layer when electron excited;

the total thickness of, and the interrelationship between 2,0 said layers in, a said medium being such that (f) said silver halide layer is adapted to form a latent image upon exposure to a preselected radiant energy pattern; (g) said silver halide layer is further adapted to be chemically developed as part of said medium following exposure to said preselected radiant energy pattern; and (h) said fluorescent layer is adapted t-o emit photon energy when one face of a said medium is bombarded by electrons of predetermined minimum average energy.

10. A recording medium capa-ble yof emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons following first exposure of one face thereof to modulated radiant energy and then development of the so-exposed face to produce a selective photon energy mask corresponding to such modulation,V said medium integrally comprising in combination:

4' (a) an unexposed silver halide layer compris-ing a radiation sensitive silver halide emulsion having a uniform silver content of at least about 500 milligrams per square meter of surface area;

(b) a scintillator layer (l) comprising a fluorescent composition capable of photon energy emission when excited by impinging electrons, andy (2) characterized by having a persistence time not longer than about l06 seconds, 4

(c) a conductive layer comprising an electrically conductive material having a surface resistance less than about l08 ohms per square;

(d) a supporting layer comprising a grain-free sup-Y porting material;

(e) said silver halide layer being distinct from said other layers;

(f) when any one of said other layers is positioned between said silver halide layer and said fluorescent layer, .such layer is capable of transmitting at least 20% of the photon energy emitted by said fluoroescent laye-r when electron excited; v v

the total thickness of, and the interrelationship between said layers in, a said medium being such that (g) said silver halide layer is adapted to form a latent image upon exposure to a preselected radiant energy pattern;

(h) said silver halide layer is furtheradapted to be chemically developed as part of said medium following exposure to said preselected radiant energy pattern; and i (i) said fluorescent layer is adapted to emit photon energy when one face of a said medium is bombarded by electrons of predetermined minimum A aver-age energy.

11. A recording medium capable of emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons following first exposure of one face thereof to a radiant energy pattern and then development of the so-exposed face to produce a selective radiant energy mask corresponding to such modulation, said medium integrally comprising in combination:

(a) an unexposed silver halide layer comprising a radiati-on sensitive silver halide emulsion having a uniform silver content of at least about 500 milligrams per square meter of surface area;

(b) a fluorescent layer (l) comprising a fluorescent composition capable of photon energy emission when excited by impinging electrons,

(2) characterized by having a persistence time not longer than about 6 seconds, and

(3) further characterized by having, when par- Iticulate in nature, average individual grain sizes less than about l micron in maximum dimension;

(c) a conductive layer comprising an electrically conductive material having a surface resistance less than about 108 ohms per square;

(d) a supporting layer comprising a grain-free supporting layer;

(e) said silver halide layer being distinct from said other layers;

(f) each of said other layers being on the same side of said silver halide layer and in any sequence; and

(g) when said conductive layer .is positioned between said silver halide layer and said uorescent layer, it is capable of transmitting at least of the photon energy emitted by said fluorescent layer when electron excited;

the total thickness of, and the interrelationship between said layers in, a said medium being such that (h) said silver halide layer is adapted to form a latent image upon exposure to a preselected radiant energy pattern;

(i) said silver halide layer is further adapted to be chemically developed as part of said medium following exposure to said preselected radiantenergy patern; and

(j) said uorescent layer is adapted to emit photon energy when one face of a said medium is bombarded by electrons of predetermined minimum average energy.V

12. A medium as described in claim 11, bearing recorded infomation therein in which silver is present in v the silver halide layer in the form of a pattern.

13. A recording medium bearing pre-recorded information capable of emitting photon energy differentially from one face thereof in response to bombardment of one face thereof with excited electrons, said medium integrally comprising in combination:

(a) an emulsion layer as the top functional layer cornprising a plurality of silver deposits arranged in an image-wise pattern in an emulsion;

(b) a fluroescent layer comprising a fluoroescent composition capable of photon energy emission when excited by impinging electrons;

(c) a conductive layer comprising an electrically conductive material;

(d) a supporting layer comprising a grain-free supporting material;

(e) said silver halide layers being distinct from said other layers;

(f) when any one of said other layers is positioned between said silver halide layer and said fluorescent layer, such layer is capable of transmitting at least 20% of the photon energy emitted by said fluorescent layer when electron excited.

14. A recording medium bearing pre-recorded information capable of emitting photon energy dilferentially from one face thereof in response to bombardment of one face thereof with excited electrons, said medium integrally comprising in combination:

(a) an emulsion layer as the top functional layer comprising a plurality of silver deposits arranged in an image-wise pattern in an emulsion;

(b) a fluorescent layer comprising a fluorescent composition capable of photon energy emission when excited by impinging electrons;

(c) a conductive layer comprising an electrically conductive material;

(d) a supporting layer comprising a grain-free supporting material; (e) said silver yhalide layer 4being distinct from said other layers;

(f) each of said other layers being on the same side of said silver halide layer and in any sequence; and (g) when said conductive layer is positioned between said silver halide layer and said fluorescent layer, it is capable of transmitting at least 20% of the phot-on energy emitted by said uorescent layer when electron excited.

15. A process for information storage comprising the steps of:

(a) differentially irradiating -a surface of a sheet-like storage medium initially capable of emitting photons uniformly from a surface thereof in response to uniform electron excitation of a surface thereof, and initially capable of chemically and internally altering its ability to radiate photon energy from one surface thereof upon exposure of that surface to said differential irradiation, thereby creating a latent image-wise pattern in said irradiated surface, said medium cornprising a discrete undeveloped silver halide layer of a multi-layer construction including in addition a fluorescent layer and a conductive layer;

(b) subjecting the so-irradiated surface to development so as to create an image-wise pattern of silver deposits within said medium adjacent the so-irradiated surface thereof; and

(c) subsequently exposing a surface of the resulting storage medium to uniform electron excitation so as to cause one surface of the so-developed storage medium to produce photon emission differentially in a manner representa-tive of said initial differential irradiation.

References Cited by the Examiner UNITED STATES PATENTS 2,748,288 5/ 1956 Saulnier 250-65 3,045,117 7/1962 Beatty Z50-65 3,195.110 7/1965 Nail 250-219 RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner. 

15. A PROCESS FOR INFORMATION STORAGE COMPRISING THE STEPS OF: (A) DIFFERENTIALLY IRRADIATING A SURFACE OF A SHEET-LIKE STORAGE MEDIUM INITIALLY CAPABLE OF EMITTING PHOTONS UNIFORMLY FROM A SURFACE THEREOF IN RESPONSE TO UNIFORM ELECTRON EXCILIATION OF A SURFACE THEREOF, AND INITIALLY CAPABLE OF CHEMICALLY AND INTERNALLY ALTERING ITS ABILITY TO RADIATE PHOTON ENERGY FROM ONE SURFACE THEREOF UPON EXPOSURE OF THAT SURFACE TO SAID DIFFERENTIAL IRRADIATION, THEREBY CREATING A LATENT IMAGE-WISE PATTERN IS SAID IRRADIATED SURFACE, SAID MEDIUM COMPRISING A DISCRETE UNDEVELOPED SILVER HALIDE LAYER OF A MULTI-LAYER CONSTRUCTION INCLUDING IN ADDITION A FLUORESCENT LAYER AND A CONDUCTIVE LAYER; (B) SUBJECTING THE SO-IRRADIATED SURFACE TO DEVELOPMENT SO AS TO CREATE AN IMAGE-WISE PATTERN OF SILVER DEPOSITS WITHIN SAID MEDIUM ADJACENT THE SO-IRRAIDIATED SURFACE THEREOF; AND (C) SUBSEQUENTLY EXPOSING A SURFACE OF THE RESULTING STORAGE MEDIUM TO UNIFORM ELECTRON EXCITATION SO AS TO CAUSE ONE SURFACE OF THE SO-DEVELOPED STORAGE MEDIUM TO PRODUCE PHOTON EMISSION DIFFERENTIALLY IN A MANNER REPRESENTATIVE OF SAID INITIAL DIFFERENTIAL IRRADIATION. 